Operating principle
Operating principle of heat pumps
The heat pump performs the following energetic task: absorbs heat from the low-temperature environment (air, water or ground) and makes it usable at a higher temperature, e.g. in a building. So we can tell that it “pumps” the heat from the environment to the usable temperature, through investing external energy. In almost every place we can find a suitable heat source which can be efficiently utilized energetically only by means of heat pump and we need not even purchase the heat carrier.
Certain designs of heat pumps can be used for not only heating but also cooling in an energy saving way. So with this solution the cost of the traditional air conditioner unit to be installed separately can be saved.
From the figure it can be seen that the elements of the system constitute
The operating principle can also be well illustrated with the figure:
• in the evaporator utilizing the earth heat (green heat), the cooling medium which is by several degrees colder than the momentary earth heat absorbs heat under the effect of the temperature difference. As a result of the increase of the enthalpy (heat content), the cooling medium will go through change of state. The cooling medium of liquid state will take steam state of condition when it leaves the evaporator. Its temperature, however, will almost the same between and after the evaporator.
• the cooling medium of an enthalpy increased by the ground heat or waste heat (green heat) but low temperature being in gas state of condition will get in the compressor where it will compress the cooling gas through the input of electric power. The pressure and temperature of the cooling medium will significantly increase and the enthalpy will grow further with the electric power input (kWh).
• the high-pressure steam of the working medium will get in the condenser, where the working medium will transfer its heat which gained from the ground heat and the electric power input to the heat absorbing medium of lower temperature, while precipitating. Its temperature, however, will be almost the same when entering the condenser and leaving it (high temperature).
• Now in the expansion valve, the pressure of the already liquid-state working medium will decrease from the pressure of the condenser to the pressure of the evaporator. The cycle will be repeated by the working medium’s flowing into the evaporator.
Operating principle of VAPORLINE heat pumps
It is similar to the schematic cycle. The difference is in the reversible cycle, the EVI (Enhanced Vapour Inject) compressor to be used for special heat pump applications and the economizer included in the cycle as well as the expansion valve of the economizer, the vapour pipe and the auxiliary devices. The economizer (cooling agent – cooling agent heat exchanger) included in the cycle has double effect:
1. It will forward cooling medium vapour of increased enthalpy and low temperature into the compressor, and thereby decreases the temperature of the overheated cooling medium.
2. It will produce strong after-cooling, which will improve the efficiency of the cycle.
Result of all these:
- Higher output
The improvement of the output is achieved rather through increasing the enthalpy of the system than by growing the mass flow. It is achieved without increasing the actual displacement.
- Increased COP
Power efficiency increases as a result of the fact that the increase of the actual output is greater that the increase of the power required by the compressor.
- Favourable cost and power consumption
The more favourable cost results from the fact that a compressor of smaller dimension than that of the traditional system can be applied for reaching the same output.
- Higher condensation temperature can be achieved.
Desuperheater
For the reversible (heating-cooling) types of VAPORLINE heat pumps, we apply a primary double tube heat exchanger (desuperheater) of special design and manufacture for the production of domestic hot water. This heat exchanger uses the superheat of the cooling cycle for producing DHW. (See: T-S diagram, Points 1, 2, 3)
Between Point 1 and 2: compression of dry, saturated cold steam. The compression occurs in the superheated range at Point 2.
Between Point 2 and 3: calorific output at p2=permanent pressure until the boiling point temperature is reached. This is the heat amount that can be used for producing domestic hot water by means of the primary heat exchanger (desuperheater) installed just after the compressor (see Figure 9). This heat amount is 12-15% of the total output of the cycle.
Application of the desuperheater is favourable mainly for reversible (heating/active cooling) heat pumps since by this solution we can produce DHW free of charge with the heat withdrawn from the building.
Its other advantageous feature is that the average cooling agent temperature of this section is higher than the condensation temperature and therefore higher DHW temperature can be achieved at optimum condensation temperature.
Its disadvantage is that DHW production can occur only if the appliance works in heating or cooling mode. During the transitional season additional heating (sun collector, electric coil) must be provided.
For systems of higher DHW demand, we can solve DHW production from the condenser as well through the installation of a direct DHW heat exchanger (double condenser). The great advantage of the device is that in this case 55-600C DHW temperature can also be achieved.
Cooling agent receiver /receiver/
When designing Vaporline heat pumps, the primary aim is to maximize and stabilize the COP value. A simple but useful part, the receiver serves this aim. Its characteristics:
It solves the appropriate aftercooling on the liquid side and modulates the amount of the cooling agent in the cycle.
It compensates the necessary cooling agent difference between the heating and cooling mode in all ranges or in an actual range of operation.
It helps in achieving higher system output at higher evaporation temperature levels.
Information on the test:
The test is made at 50% capacity and with a compressor of 6sec cycle time. In the event of using 3kg cooling agent receiver, the output pressure change was 0.25 Mpa in the cooling agent receiver.
If the dimension of the liquid receiver is greater, than the pressure change will be less.
As a result of the decreased pressure change, the stable flow of the cooling agent to the EEV valve is ensured. It will help in increasing the system output.
The figures demonstrate that the greater cooling agent receiver will result in lower Dp-t and further increase of system performance.
